The hydroformylation of ethylenically unsaturated compounds to form aldehydes and/or alcohols, is of considerable industrial importance. The process has been in commercial operation for decades and over the years much development work has been done to optimize the reaction conditions, the catalyst system and the equipment.
Although significant progress towards higher yield and product selectivity has been made, further improvement of the process is still needed.
In EP-B 0 495 547 there is disclosed a monocarbonylation process whereby the catalyst system comprises a source of palladium cations, a source of anions, and a bidentate diphosphine as defined below. In hydroformylating olefins, the activity and selectivity of this catalyst system is still not entirely satisfactory.
In WO 95/05354 there is disclosed a hydroformylation process whereby the catalyst system comprises a source of platinum group metal cations, a source of anions other than halide anions, a source of bidentate ligands as defined below and a catalyst promoter comprising a source of halide anions in a molar ratio halide anion: platinum group metal cation of at most 3:1. It is shown that the presence of the halide ion accounts for a considerably enhanced activity and selectivity of the process towards the desired alcohol products. However, this process appears to be exceedingly sensitive to small variations in halide ion concentration, the positive effect of which having a sharp peak at a molar ratio to the cation of about 0.4:1. In Examples 10-12 of WO 95/05354 tin chloride was the promoter used and water was added to an amount of 0.6 wt %, calculated on the total of the reaction mixture. However, any particular effect of the water was not recognised and cannot be deduced from this document.